ORLANDO, Fla. - A piece of World War II ordnance caught fire at a Florida middle school, days after parents were told the grounds were completely clear.

"Every day I come here is an absolute nightmare," one tearful woman told the Orlando Sentinel as she dropped off her daughter at the Odyssey Middle School in Orlando.

The school was built on part of a bombing range. In the past five months, the U.S. Army Corps of Engineers has removed about 100 live bombs and tons of bomb debris from the school grounds and some neighboring properties at a cost of $1 million.

Nancy Stitch, a spokeswoman for the Corps, said the school grounds are safe. A spokesman for the school district agreed, saying the piece that caught fire was in an area where the Corps is still working.

Workers said an employee of a subcontractor found part of a phosphorus bomb, which ignited when it was exposed to air. The employee was treated at a hospital and released.